I. Technical Field
The present invention relates to sealing devices for rotary fluid machines and to rotary fluid machines.
II. Description of the Related Art
In general, rotary machines that compress or expand fluid, such as centrifugal compressors or expanders, use a seal such as a labyrinth seal in order to prevent a fluid leak from a high-pressure portion to a low-pressure portion.
The labyrinth seal is disposed between a fixed part such as a housing and a rotating part such as a rotary shaft, and a seal gap is provided between the labyrinth seal and the rotating part or between the labyrinth seal and the fixed part, in order to ensure the rotation of the rotating part.
A small amount of fluid leaking from the high-pressure portion to the low-pressure portion flows through the seal gap, and the leakage flow includes velocity components in the circumferential direction of the rotary shaft under the influence of the rotation of the rotary shaft. Hereinafter, the leakage flow that includes velocity components in the circumferential direction is referred to as swirling flow.
If a swirling flow exists in the seal gap, it is known that an exciting force that disturbs the behavior of the rotary shaft, that is, a destabilizing force, may occur. It is known that the destabilizing force increases when the difference in pressure between the high-pressure portion and the low-pressure portion in the rotary machine increases.
In order to solve such a problem, technologies of providing guide grooves or guide blades for canceling or eliminating the velocity components in the circumferential direction of the rotary shaft included in the swirling flow have been proposed (for example, see Japanese Unexamined Patent Application, Publication No. S58-022444 and Publication of Japanese Patent No. 2756118).